1. Field of the Invention
The present invention relates to an abrasive employed in blast processing and a blast processing method employing the abrasive. More specifically, the present invention relates to an abrasive for blast processing employed for processing a surface of a workpiece by blast processing so as to provide a smooth finish, a mirror-like finish, a luster-like finish, a glossy finish, etc., and to a blast processing method employing this abrasive in order to provide a smooth finish, a mirror-like finish, a luster-like finish, a glossy finish, etc.
Moreover, the “blast processing method” of the present invention not only includes an air blasting method, such as a wet blasting method or dry blasting method, in which a compressed fluid containing compressed air, etc. is utilized in the ejection of the abrasive, but may also include a wide variety of blasting methods whereby the abrasive is ejected at a predetermined ejection speed and ejection angle with respect to the processing surface of the workpiece, such as a centrifugal-type method (impeller-type), in which an impeller is rotated to provide centrifugal force to the abrasive for ejection thereof; or a stamping-type method, etc., in which a stamping rotor is used to stamp down on the abrasive for the ejection thereof.
2. Description of the Related Art
In a process in which a tool bit, an end mill, a milling cutter, a gear hob, a broach, etc., is employed as a cutting tool, the area that can be cut in one pass is limited by the dimensions of the geartooth width of the cutting tool, etc. Accordingly, when a cutting process is conducted on a relatively large area on the workpiece, the cutting tool must be repeatedly fed at a predetermined pitch, and the process must be continued a plurality of times, in order to widen the cutting area thereof.
Therefore, in a processed cut surface of a product that was cut in said manner, processing indentations, referred to as “cut marks” or “tool marks”, etc., arise in response to the feed pitch of the abovementioned cutting tool, causing uneven portions ranging from a few microns up to 1 mm to be formed therein (see FIGS. 1, 4 and 5).
When the product in which these processing indentations have occurred is assembled as is into a device as a component thereof, etc., the irregularities among the uneven portions that were caused by processing indentations during the continued usage of said device are worn down and cut, to reduce a protruding length thereof. Accordingly, the overall size of said component is also reduced, which thereby generates excessive clearance between the product and other elements and leads to problems, such as being unable to achieve the desired performance.
Thus, as described above, the processing indentations that occurred during the cutting process must be removed, in order to flatten the surface of the product after the cutting process.
Moreover, when the object of processing is a metal mold, the processing of this mold is generally conducted via a cutting process performed by a machining center, or an electro-discharge machining method. However, since the surface roughness of a mold that is processed by these methods is increased after the surface of the mold is processed via a machining center or electro-discharge machining, it must be smoothed to the desired surface roughness.
This smoothing process is conventionally conducted by polishing with an abrasive, such as abrasive paper or abrasive cloth, or a grindstone, etc.; or polishing with a buff; lapping; polishing by the contact between rotating abrasive grains; polishing by the contact between abrasive grains to which an ultrasonic vibration has been applied, etc. However, since these operations are typically performed manually, they require a skilled operator, as well as a considerable amount of time.
Moreover, the condition of the finished product differs depending on the skill of each respective operator. Furthermore, when the product to be treated has a complicated shape, the processing thereof becomes extremely difficult. Accordingly, the automatization of these flattening processes, a reduction in the costs thereof, and the prevention of variations in processing accuracy are also needed.
In addition, with regard to a metal mold for injection molding to resin, an edge portion of a parting surface of the metal mold is sometimes lost thus rounded depending on the method of manufacturing the metal mold. Therefore, when injection molding is performed using such mold, the resin injects into the edge portion thereof, as a result, irregularities or linear burrs are formed in the portions into which the resin injects after the molded product is released.
The irregularities or burrs that arise in the molded product are manually removed by an operator after molding, by cutting with a cutter or buffing out. However, not only is this manually operated process inefficient, but it is also unsafe, especially since this operation for removing the burrs or irregularities with a cutter risks injury to the operator of the cutter.
Accordingly, the development of a method whereby the above-described burrs or irregularities can be safely and efficiently removed is also highly desirable.
Moreover, by employing the blast processing in procedures such as polishing a surface of the metal mold and removing burrs, etc. that occur in the product, it allows the removal of burrs and polishing via the cutting force of the ejected abrasive grains. Said blast processing can be applied relatively easily, even in cases where the product to be treated has a complex shape.
However, with regard to the surface of a workpiece treated by a conventional blast processing method, when the abrasive grains are bombarded therewith, indentations are formed in the surface of the product. Therefore, since these indentations cause the formation of a satin-like finish on the surface, the blasting process cannot be applied to the desired objectives of smoothing the surface of the product after processing or providing the product with a mirror-like finish, but even if it could be applied, it would require a process whereby the satin-like finish that occurred from the blasting process after burr removal, etc., is additionally processed.
Accordingly, when conventional blast processing is performed, the surface of the product to be treated is provided with a satin-like finish, so that a smooth finish, mirror-like finish, luster-like finish, or glossy finish cannot be applied to the processed surface of the workpiece. On the other hand, a blast processing method that can be performed relatively easily, regardless of the shape of the product to be treated, etc., has the distinct advantage of being applicable even when the shape of the product to be treated is a relatively complicated shape.
Thus, the present invention provides a novel abrasive for blast processing in which a smooth finish, a mirror-like finish, a luster-like finish, or a glossy finish is applied to the surface of the product to be treated, and a blast processing method employing this abrasive.
Moreover, a method for blast processing has also been proposed, in which an abrasive grain carried on a carrier consisting of an rubber elastic body, etc. (hereinafter, the abrasive in which an abrasive grain is carried on the elastic carrier in this manner will be referred to as “elastic abrasive”) is employed, and by ejecting this elastic abrasive onto the surface of the product to be treated at an angle, the impact from the abrasive colliding with the product to be treated is absorbed by the elastic deformation of the carrier, to prevent the formation of indentations, and thus a satin-like finish, and to allow the abrasive to slide along the surface of the product to be treated, so that a flat, or mirror-like finish, etc., can be provided.
Moreover, with respect to said carrier formed of rubber, serving as said elastic body is a grinding method for grinding the surface of a workpiece with an abrasive powder by ejecting abrasive gains onto the surface of a workpiece at an angle oblique thereto, the abrasive grains being produced by adhering the abrasive powder to elastic porous carriers formed of natural vegetable fibers, and then mixed with an abrasive liquid, to impact on the surface of the workpiece, causing the abrasive grains to slide on the surface of the workpiece while the abrasive grains are allowed to deform (see Japanese Unexamined Patent Application Publication No. H9-314468, claim 1).
According to the abovementioned method, the abrasive grains slide on the surface of the workpiece by the lubricating action of the grinding liquid while elastically deforming the carrier when impacted on the surface of the workpiece, so that the workpiece can be smoothly finished over the distance the abrasive grains traveled (see Japanese Unexamined Patent Application Publication No. H9-314468, Paragraph [0006]).
Furthermore, with regard to the configuration of the elastic abrasive, problems exist in that when a carrier is formed of rubber, the surface of the product to be treated becomes satin-like (Japanese Patent No. 3376334, Paragraph [0003]), and when a carrier is formed of vegetable fibers, even though the surface to be abraded of the product to be treated is polished almost to a mirror-like finish when the carrier contains water, once the water within the carrier evaporates from heat generated at the time of polishing, thus reducing the elasticity and viscosity of the carrier, the product to be treated is provided with a satin-like finish, and the recovery rate of the carrier is decreased because of breakage of the carrier (Japanese Patent No. 3376334, Paragraph [0004]). Thus, a blast processing method employing an elastic abrasive is provided, in which an elastic abrasive comprises water-retaining carriers, onto which abrasive grains are adhered by the adhesive force associated with the water contained therein, the water-retaining carriers being formed of a gelatin containing an evaporation preventing agent (Japanese Patent No. 3376334, claim 1, and Paragraph [0004]).
As mentioned above, in a blasting method employing an elastic abrasive of the above-described conventional art, by employing an elastic abrasive in which an abrasive grain is carried on a carrier body, which is an elastic body, indentations are formed on the surface of the product to be treated, even when the elastic abrasive bombards with the product to be treated as a result of elastic deformation of the elastic abrasive. Accordingly, by sliding the elastic abrasive along the surface of the product to be treated, while preventing the surface of the product to be treated from becoming satin-like, a predetermined polishing process can be performed.
Thus, by performing the blast processing using the elastic abrasive, a luster-like finish or glossy finish can be provided to a post-processed surface of the product to be treated, and, when blast processing in conducted to a product in which processing indentations occurred in response to the feed pitch of the cutting tool, the height from the bottom of a valley (maximum valley depth) to the peak (maximum peak height) of the surface roughness can be reduced, so that the surface thereof can be made relatively flat with respect to the pre-processed surface condition.
However, with regard to a post-processed surface of a product in which the elastic abrasive is employed, as described above, even though the height of the roughness curve from the bottom of the valley to the top of the peak can be reduced, the appearance of the pattern of the peaks and valleys of the pre-processed roughness curve remains the same, even after processing.
Afterwards, it was confirmed that the depth of the valleys of the surface roughness of the post-processed product was deeper than that of the valleys of the surface roughness of the pre-processed product, and therefore, not only were the peaks removed but the valleys were also cut deeper (refer to FIGS. 2 and 3).
The problem with blast processing employing this type of elastic abrasive is that, in order to completely eliminate all the irregularities in the surface of the product to be treated, along with cutting the peaks of the roughness curve, the valleys are also inevitably cut away, and thus deepened.
Moreover, if the processing time is increased in order to eliminate the surface irregularities, the amount of a product to be treated that is cut away is also increased, therefore making it difficult to process the product to be treated with the correct finished dimensions.
Accordingly, an object of the present invention, which has been made to solve the above problems of the related arts, is to provide the abrasive for blast processing and the blast processing method employing this abrasive, which is capable of eliminating the irregularities in the surface of a product to be treated that are difficult to eliminate by a conventional elastic abrasive, but also to prevent the formation of a satin-like finish on the surface of the product to be treated, in cases where the elastic abrasive of the present invention is employed.